Biomedical Engineering Reference
In-Depth Information
were also found virulent (Amiri-Besheli et al. 2000). Toxin profi le was
found to determine the host range of a fungal strain. Intra and interspecifi c
variation in the toxin profi le and quantities of toxin produced was found in
Metarhizium
spp. (Amiri-Besheli et al. 2000). Certain strains of
M. anisopliae
secrete destruxins immediately after entering the hemocoel causing
toxicemia and immediate death while some do not produce destruxins but
grow profusely in the hemocoel and cause slow death (Amiri-Besheli et
al. 2000). Very low levels of destruxins suffi cient to anaesthetize the insect
but not causing death were detected in the hemocoel of infected insects
(Amiri-Besheli et al. 2000). It was suggested that the quantity and type
of destruxin secreted could play an important role determining virulence
and/or specifi city for some strains of
Metarhizium
(Amiri-Besheli et al.
2000). Genes for non ribosomal peptide synthetases have been identifi ed
(Gao et al. 2011, Takahashi et al. 2007; Doekel et al. 2008). Toxins have been
found to be responsible for death of the insect along with other factors
affected by infection. Behavioural symptoms in fungal infected insects
like partial or general paralysis, sluggishness and decreased irritability
indicate the action of neuromuscular toxins (Charnley 1984).
Other toxins may also be synthesized in entomogenous fungi. In
B.
bassiana
, an EST homologous to P450 monooxygenase was detected when
cultured on insect cuticles but not when cultured on synthetic medium
(Khan et al. 2007). Cytochrome
P450 monooxygenase is reported to mediate
reactions for major nuclear rearrangement steps in the production of toxins
in
Aspergillus nidulans
(Keller et al. 2000) and
Fusarium
sporotrichioides
(Alexander et al. 1998). Production of these toxins has been reported to
enhance the virulence of
Fusarium
(Alexander et al. 1998).
Mycosis on Cadaver
A regulator of G protein signaling gene involved in conidiogenesis
(cag8
),
a subtilisin-like protease pr1 and a hydrophobin gene (
ssga
) were found
through qRT PCR studies to be highly expressed during mycosis on the
insect cadaver (Fang and Bidochka 2006). qRT-PCR results showed that
Pr1 is produced during the initial stages of trans cuticular penetration by
M. anisopliae
and also up regulated during the fi nal stages of pathogenesis
as the fungus emerges from the dead host and subsequently conidiates on
the cadaver (Fang and Bidochka 2006, Small and Bidochka 2005).
Virulence Genes
A superoxide dismutase (SOD) was characterized from
Beauveria bassiana
.
The gene
BbSod2
characterized as a Mn-SOD in
B. bassiana
was shown
